Damp problems due to ground height?

[John P72]

Hi,

I'd really appreciate some advice on a long running damp problem I've had in my house. I'm an end of terrace and along the external wall there has been a history of damp. The previous owners had it drilled and injected, and I've also had an area injected and rendered with the special plaster to prevent damp. However, despite this it appears that some of the damp has "jumped" over the treated area and is now appearing higher up on the wall inside.

I believe that the underlying problem may be the path height in the side alley that runs along the side of the house. I've attached photos that show at the front end of the alley the plinth is only 2" high and at the back of the house the plinth is around 7". Also the airbrick is below the path height (whereas looking at my neighbours houses the airbrick is all above ground level).

Therefore, I was thinking of either dropping the path height so I have a uniform height of around 7" and the airbrick above ground level. Or digging a gully along the side of the wall perhaps 6" deep and filling with pea shingle to allow extra drainage - although with this option the air brick will still be a problem.

So a few questions:
- From the attached photos do you think the path height is the reason? Or something else?
- What is the better solution - dropping the path (more work) or the gully?
I welcome any advice!

Many thanks
John

 

[dontbelieveawordofit]

The damp problem runs across the whole wall? or is it localised inside the house?
is it your path on your property?

 

[ted456]

can you post photos showing ground level at front back and side elevations?
is all the walls solid or cavity and is all the floors suspended or mixed solid and suspended?
and photos of inside showing the damp signs?

DPC's should be set under the air brick and under joist tails supported in the wall.
the path is too high and its bridging your DPC.
the render is allowing moisture to be sucked up from ground contact. so is the fillet and plinth of mortar.
a french drain will still be bridging your DPC

 

[John P72]

Thanks for the replies. So to add a bit more information:

"The damp problem runs across the whole wall? or is it localised inside the house?"
=> The damp appears only on the inside walls of the house. The external wall is pebble dash and has sandtex exterior paint so I guess it forces it through onto the inside. The damp only appears in small patches with the worst area under the staircase (which has the boiler / gas meter / elec meter) - see photo. The previous owners had placed wooden boarding against the wall (probably to hide it)! Also in a downstairs WC where the spots appear at a height of between 80cm and 120cm - hence my comment on "jumping over" the previously treated area. Photos attached.

"is it your path on your property?"
=> Yes the path is on my property. It's not well ventilated though as it has a gate at both ends. Photo attached.

"can you post photos showing ground level at front back and side elevations?"
=> I've posted a photo of the front of the house and the airbricks seem higher than at the side of the house (even with block paving). At the rear of the house there is a conservatory (which has 2 air bricks) which are well above ground level and there is no damp in the conservatory (other than the roof leaking!).

"is all the walls solid or cavity"
=> Solid

"is all the floors suspended or mixed solid and suspended?"
=> Sorry I don't know how to tell that? It's a 1930's end of terrace

From the response I'm gathering the gully / french drain won't work and lowering the path is the best option? If so, when concreting a new path should I concrete up to the side of the house perhaps with a slight angle away to drain water away?

Thanks for your help!

 

[ted456]

1930's usually have a cavity but with a solid wall maybe the damp is penetrating the render and the nine inch wall
The high path bridging the DPC might be part of the problem.
At the front of the house the air bricks are to high and the mortar plinth needs removing - all mortar plinths need shifting.

Solid floors are concrete floors - usually in the kitchen, and suspended floors have a space below them that needs through ventilation.
thats why you have air bricks that should be fixed below the DPC.
your front and probably rear air bricks are to high.
Seeing you have damp and hig paths then you will need to see if your suspended floor joists are not damaged by the damp or lack of ventilation.

All plaster showing damp should be removed down to the floor and made good with render not plaster. Ditch the wood panelling.
All render with ground contact to be cut back.
You need to examine inside walls at ground/FFL levels looking for cracks or damp.
and examine render for cracks or blown areas.

 

[nick fisher]

first ill address the outside level .. Yes the outside paved area / paths are way to high, should be at least 150mm from the damp course to the path surface.. ( damp course is bed joint under the air brick ) 150mm is about two bricks plus bed joint (The bed joint being the bed of cement bricks sit on) . This is so common the house is nearly 100 years old and has had multiple path's put on top of each other . for the side of the property .. the only solution is to dig it all up sadly lay a new path at a suitable height.. French drain is a big no no it will encourage water to sit against your property ( a french drain is dug into the ground a pipe laid with gravel . . A channel drain is much better which is what i suspect you might have been thinking about . .. if you start with the side of the house you will get an idea about how deep you have to go . . . i see from your pictures you will have to deal with the soil waste (toilet pipe) . you will also have to pinpoint all your services . water gas electric . and waste . just be weary about where you start digging away . That should be where you start with this problem, ..

 

[rougharsedbrickie]

first ill address the outside level .. Yes the outside paved area / paths are way to high, should be at least 150mm from the damp course to the path surface.. ( damp course is bed joint under the air brick ) 150mm is about two bricks plus bed joint (The bed joint being the bed of cement bricks sit on) . This is so common the house is nearly 100 years old and has had multiple path's put on top of each other . for the side of the property .. the only solution is to dig it all up sadly lay a new path at a suitable height.. French drain is a big no no it will encourage water to sit against your property ( a french drain is dug into the ground a pipe laid with gravel . . A channel drain is much better which is what i suspect you might have been thinking about . .. if you start with the side of the house you will get an idea about how deep you have to go . . . i see from your pictures you will have to deal with the soil waste (toilet pipe) . you will also have to pinpoint all your services . water gas electric . and waste . just be weary about where you start digging away . That should be where you start with this problem, ..

Rofl. Airbrick can be either above or below dpc, age of property gauge is not 75mm, a joint bed or prep is not cement but mortar and the only reason a french drain would not be suitable is if it was incorrectly constructed. Really

 

[nick fisher]

An Imperial brick typically measures 225mm by 110mm by 65mm (or up to 70 or 80 in the north of England) from the pictures Looks about 75 ish to me .. Iam guessing you ment perp as in perpendicular joint .. not prep .. And yes it's mortar and not cement .. But it was trying to write it in laymen and it's common for people not in the trade to call it cement .. he was talking about putting a french drain against the property that's bad practice . everyone knows a french drain is laid at the lowest point and should carry water away from the building not run alongside abut the footing . effectively creating a low point which runs along the property ..The trench should go in at least two feet below your substructure soil level. Digging the trench too close to the house can complicate your problems. A good rule of thumb is moving the drain one foot off the wall for each foot down you dig; for a four-foot deep drain, build it four feet from your walls... and judging from the picture the dpc is under the air brick . as the old ruff cast / pebble dash stops at the top of the air brick . and the level of the 4 inch waste . . so if the air brick was below the dpc then the dpc would be breached right ... roflmao .. Every job is different and im just going off the evidence i see in the pictures ..

 

[rougharsedbrickie]

Nice cutting and pasting from google guess I dreamt laying the 45mm and 60mm bricks. And the dpc is breached . Better advice would be to lose the render ‘ plinth’ and the roughcast from the bottom of the wall to let it breathe. Ever heard of a footing drain ? Pml

 

[stuart45]

When I started on site the trade was just going metric. Bricks had been a standard size for a few years at 9x4.5x3 inches which included the 3/8 joint. Metric sizes were as close to this brick as possible. Before that brick sizes varied a fair bit.

 

[John P72]

Thanks for the replies as it confirms that the path is too high.

My description my might have caused confusion but to confirm there is no damp at either the front or rear of the house. Only at the side of the house where the path runs along the external wall.

I'm keen to try the less expensive and easier approach first, and so when I mentioned digging a gulley against the side of the wall the aim was to prevent the path from bridging the DPC as the guley would prevent this and provide improved drainage with the stones. As opposed to filling the gulley with stones could I use a paving drainage and grate as per below. Would that be better?

https://www.diy.com/departments/cla...inage-grate-l-1m-w-142mm/5016609124288_BQ.prd

Thanks
John

 

[noseall]

there is no damp at either the front or rear of the house. Only at the side of the house where the path runs along the external wall.

A lot of the damp will be because of the conditions arising from the narrow 'trapped' environment. Extra dilligence is required where standing water has little chance to evaporate and is likely to remain there for long periods, especially during the cooler months.

For example, I would try and introduce a storm drain gulley (or two) and have all rainwater falling towards them. The fact that the render is wicking the water and the fact that there is little chance of sunlight on that wall, just adds to the issue that the wall was built poorly (poor by todays's standards), leading to the problems you have now.

 

[JohnD]

A French Drain filled with cobbles or pebbles does not pull water into the wall, because the gaps are too big for capillarity.

Water will rise through the fine pores of soil or sand. Clean no-fines gravel is not so bad but pebbles are best.

Also, of course, the drain itself will be leading excess water away, and water can drain through clean cobbles.

The position you show also has a drain or sewer alongside the house, and water pipes, which could be leaking and providing more water to worsen damp. You will find out when you start to dig.

 

[ted456]

Youve still not said where the DPC is?

The DPC goes under any joists supported in the wall, the joists sit on the DPC. Its best if the air brick goes below the DPC that way any joist thats running parallel and tight to the wall wont be blocking ventilation. But setting the air brick on top of the DPC between the joists is common when the brickie knows the joist direction..
A French drain wont work, how deep do you want to dig it? Where will it lead excess water away to? After lots of work and expense, Aco drains could lead to a rear elevation gulley?
The fly in the ointment for any drainage idea is the soil pipe.
If you dig out and drop the path you will be lower than the other side of the fence and the front and rear ground levels.
The front block standing is to high, the rear ground level is ...?

If theres no damp issues at the front then why the painted brick and the mortar plinth? The flank wall render was done to prevent damp
Theres what looks like a redundant external chimney breast in pic 6?
Another pic shows a unprotected cable hanging loose.

 

[John P72]

I've now dug the gully alongside the house - please see the photos.

When digging I reached the footings of the house and as mentioned before the path is on a slope, so I had to dig deeper at the front of the house (depth of 16") compared to the rear (depth of 10"). I dug out quite a lot of damp clay and sand which I doubt would have helped. I plan on leaving the gully open now for a couple of months to breathe and hopefully dry out with this warm weather. A couple of questions:

- From one of the photos you will see the render is uneven and stretches down quite low to nearly the level of the footings at some points (which again I doubt would have helped?). Should I trim this render off and perhaps take it up to the paint line level to expose the brick work and help drying?
- Whilst scraping the clay off the brickwork at the base of the gully at some points the cement between the bricks came away so I will need to refill it. Is there any special cement I should use? E.G. something with water repellent? (I'll let the bricks dry before doing this).

Thanks for any advice!